I can confirm that in m2p 2.37 when Nightly 7.9 is selected in the m2p interface, the URL that is shown contains references to 7.8 instead of 7.9. It appears that the URL shown doesn’t change when a build selection is made. Should it?

Anyway, like jemhayward I found the real URL for 7.9 and pasted it in the box instead and all was well.